Alcohol abuse has deleterious affects on almost every tissue in the body and is a major cause of morbidity and mortality worldwide. The acute actions of alcohol on cellular function are fully reversible whereas long-term alcohol intoxication can lead to irreversible tissue damage. The molecular mechanisms contributing to the onset and progression of irreversible cell injury are still poorly understood. In this application, we propose to investigate the hypothesis that adaptive changes in the phosphoinositide-dependent signaling pathway play a key role in the pathogenesis of alcohol-induced tissue injury. Our preliminary data indicate that feeding rats an ethanol-containing liquid diet (i.e., DeCarli-Lieber) for 60 days enhances the liver' sensitivity to hormones coupled to phospholipase C-. The addition of low concentrations of hormones evoked more sustained cytosolic calcium increases in hepatocytes isolated from alcohol-fed animals compared to their pairfed controls. Moreover, cells from alcoholic animals had a larger increase in inositol-1,4,5-trisphosphate (InsP3) formation following low hormone stimulation suggesting that chronic alcohol consumption altered phospholipase C- activity. Normally, cytosolic calcium increases activate mitochondrial physiology to match ATP formation with utilization; however prolonged or inappropriate calcium increases can also lead to matrix calcium overload and mitochondrial dysfunction. Mitochondrial damage is a common feature observed in chronic alcoholic patients and animal models of alcohol abuse. Mitochondrial dysfunction may increase the tissues' susceptibility to other types of injury or apoptotic stimuli. This may be particularly important in chronic alcoholics that have elevated levels of TNFa, a proinflammatory cytokine, which evokes apoptotic cell death in hepatocytes through the mitochondrial-dependent pathway. In this proposal, we will (1) characterize the alcohol-induced alterations in phosphoinositide-dependent signaling pathway, (2) determine the effects of InsP3-dependent calcium increases on mitochondrial calcium levels and energy metabolism in control and chronically ethanol-fed rats and (3) determine the effects Ca2+-moblizing hormones on TNFa-induced apoptosis in hepatocytes from alcohol-fed rats and their pair-fed controls. The proposed studies will provide new insights into the adaptive responses evoked by the sustained presence of ethanol and the associated injurious consequences for the liver.